Modulation arrangement for magnetron transmitter



Oct. 24, 1939. HOLLMANN 2,177,065

MODULATION ARRANGEMENT FOR MAGNETRON TRANSMITTER Filed Dec. 8, 1936 MODUZA TED OUTPUT MOD/1147' ED POHWTML INVENTOR H. E. HOLLMANN BY gm ATTORNEY Patented Oct. 24, 1939 MODULATION ARRANGEMENT FOR MAGNETRON TRANSMITTER- Hans Erich Hollmann,

Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphie m. b. 11., Berlin, Germany, a corporation of Germany Application December 8, 1936, Serial No. 114;737 In Germany December 9, 1935 6 Claims. (Cl. 179171.5)

The invention deals with a modulation arrangement for any type of magnetron transmitter whose tubes are provided at the ends of the plate cylinders with metallic end plates or 5 similar radial auxiliary electrodes in the interior of the plate cylinder, whether the plate cylinder itself is closed, or has a single slot, or is divided into two or a greater number of segments.

[ It is known that in such a magnetron tube with suitable auxiliary electrodes, a coaxially directed electric field component can be produced by applying various potentials to the end plates or to inner radial plates, said field components .5 forcing the electrons out of their plane of movefluent only radially directed solely by the action of the anode field, thereby causing the electrons to take a helical course. In this manner, an eflect is attained that is similar to that appearing in the magnetic field by inclination of the tube, whereby as is known, a considerable increase in the useful efiect is obtained as compared with the coaxial position. An arrange- ,ment of this type has been disclosed in Linder United States application #703,346 filed December 21,1933. In the same manner as wouldbe possible in principle to modulate the high fre-' quency energy supplied by the tube by turning the tube forwards and backwards in the mag- 3 netic field, a corresponding amplitude, modulation can be effected by varying the potentials of the end plates or auxiliary plates. To this end, a fixed biasing potential is applied to the end plates or auxiliaryv plates, and then correspond- 5 ing modulation potentials are superposed thereon in the rhythm of equal phase or opposite phase.

This method, though it is a simple one, demands special requirements of the modulation arrangement inasmuch as the end plate resistances on which the modulation potential is to act are comparatively low in case of powerful magnetron transmitters, and furthermore they have non-linear characteristics. Thus, in order to obtain optimum conditions for linear modulation, the inner. resistance of the modulation source should be low as compared with the resistance of the discharge path between the cathode and the 'end plates. This is so that the modulation potentials may remain undistorted by the non-linear load, and if high modulation potentials are required, then considerable energy should be furnished by the modulation amplifier.

The present invention has for its object to provide an energy-free end plate modulation system wherein use-is made of the teaching that in the operating stage of the transmitter, the end plates receive a highly negative charge by the electron current passing to said plates: -5 This signifies that the end plates are the source of an inner electro-motive force which can supply as such, the energy necessary for the control or modulation of the produced oscillations. To this end, it is only necessary to insert any 0 desired modulation device in the circuit of the end plates or the circuit of equivalent auxiliary electrodes, so as to be able to modulate the magnetron without the supply of additional control power. My invention will now be described in more detail, reference being made to the accompanying drawing in which Fig. 1 shows a system for modulating a magnetron discharge tube wherein the modulations are obtained by means of a buzzer; Fig. 2 shows another embodiment of the invention in which the modulations are produced by a self-shorting relay; Fig. 3 shows still another embodiment in which the magnetron is modulated by means of a relaxation oscillator, such as a gaseous'discharge tube in shunt with a capacitor; and Fig. 4 shows finally a system for modulating a magnetron discharge tube by the application to the end plate electrodes of modulating energy from any desired source of simple or complex waves.

The principle of the invention reveals itself most clearly when attempting to modulate the magnetron by a self-regulated tone producer having a constant note. The simplest apparatus of this typ is the Wagner hammer, or buzzer, which isbased upon the electro-magnetic en'- ergizing of a steel reed, diaphragm, or string. If such a buzzer S is placed in the manner shown in Figure 1, between the end plates E and 40 the cathode K of the magnetron tube T, then the inner electromotive force of the magnetron tube actuates the buzzer, and the potential of the end plates fluctuates between the zero value and the value of the free negative charge. at the moment of the current interruption. The oscillations produced in the magnetron therefore are modulated at the frequency of the buzzer.

to'the cathode is placed at a positive or negative auxiliary potential by source l2 in order to obtain the optimum control of the magnetron. The magnetron tube T may be of the type having a plate R, field producing Winding X and energizing source Y for said field. For the sake of simplicity, the heating circuits for K' have not been shown in the drawing. The modulated output will appear in the transformer 10 and may be put to any use. The plate R may be split, in which case the output circuit is connected with the two plate sections.

Another buzzer circuit by which the free charging of the two end plates shown is avoided and whereby the potential of the end plates fluctuates between two defined values, is shown in Figure 2. .This circuit distinguishes itself from the previous example only by the arrangement and operation of the buzzer which, in place of an interrupter contact, is provided with a short circuit (Elontact SC, and operates according to the principle of the steady current, i. 8., through short circuiting of the exciter winding. Thus, the circuit of the end plates is never interrupted, and only the resistance of the magnet winding is periodically connected and disconnected. By choosing a suitable biasing voltage at l2 and a sufficiently high impedance of the buzzer winding, which may optionally be increased by a se ries resistor I4, it is possible to match the potentials of the end plates obtained when the buzzer operates, with the full utilization of the magnetron generator.

These two examples are given merely to elucidate the principle of the invention. In practice, a mechanical interrupter will preferably be avoided in view of the irregularity in establishing the contact. Hence a more practical modulation system can be developed wherein the switching is obtained by means of an electron discharge path. An arrangement which in its functioning is equivalent to the mechanical buzzer and containing a glow tube for modulation purposes is shown in Figure 3. The glow tube GL lies directly in the circuit of the two end plates E, and a suitablychosen condenser C is connected in parallel thereto for the purpose of producing a definite modulation frequency. The electron current passing to the end plates charges this condenser until the ignition potential of the glow tube is reached and at this moment the condenser C will be discharged to the quenching potential across the inner resistance of GL. Thereafter the described performance will be repeated. It can thus be seen that the arrangement produces regular relaxation oscillations with a frequency depending firstly on the size of the storage condenser C, depending secondly on the, inner charging electromotive force in the magnetron tube, and thirdly on the inner charging resistance, and finally on the internal resistance of the glow tube GL. For such relaxation oscillations the general condition must be fulfilled that the charging period be large as compared with the period of discharge; otherwise a stable equilibrium will occur. The internal resistance of the glow tube, therefore, must be low as compared with the resistance of the discharge space in the magnetron. The internal electromotive force as well as the inner resistance of the magnetron are a function of the dynamic building-up performances in the tube. It thus, follows that the relaxation period likewise depends to a certain degree on the high frequency building-up conditions of the generator. If particular importance is attached to the constancy of the modulation oscillations, the relaxation oscillations can be stabilized by a series or parallel resonance circuit connected in series to the glow tube.

point have the purpose of causing an auto-modulation of themagnetron through-introduction of a self controlling modulator, or leakage resistance. But such embodiments of the invention are not practical where the magnetron generator is to be modulated, for instance, by speech waves. In such case, therefore, I have found that the self-controlling modulator may be replaced by a remotely controlled leakage resistance, and in the simplest way obviously by a grid controlled electron tube. Figure 4 shows a suitable circuit, in which the cathode of the modulation tube Rm is connected to the end plates, the latter being negatively charged, and the anode is connected to the cathode of the magnetron tube If the inner resistance of the modulation tube Rm is and the magnetron will be modutube must be present at each side of the magnetron tube. Similar conditionsprevail if radial auxiliary electrodes in the interior of the plate cylinder are to be employed for the modulation. A leakage tube can in this case however, only be used to advantage if the potential of the auxiliary electrodes has such a high positive value that a sufiicient electromotive force and a sufliciently low inner resistance are produced. If, on the contrary, the potential of the auxiliary electrodes is negative, for instance in an alternating succession with positive auxiliary plates and end plates, then at these negative auxiliary plates no inner electromotive force appears and the inner resistance is infinite. If, thus, these electrodes are to be likewise modulated, special leakage tubes become superfluous, since these electrodes can be controlled directly without consuming energy.

I claim:

1. In a signaling system, a magnetron discharge tube having an anode and a cathode, energizing circuits therefor, means for producing a magnetic field in the electron discharge zone and end plates, and independent means for automatically interrupting said circuit at a pcriodic rate, thereby-to modulate said tube.

2. In a signaling system, a magnetron discharge tube having an anode and a cathode, energizing circuits therefor, means for producing a magnetic field in the electron discharge zone of said tube, end-plates adjacent said anode, a circuit including a source of energy connected between said end-plates and said cathode, and means for rythmically modulating said discharge tube, said means including a second tube of the ionization discharge type connected in the last said circuit, and including a capacitor in shunt with said second tube. 1

3. In a signaling system, a magnetron discharge tube having an anode and a cathode, energizing circuits therefor, means for producing awaoes a magnetic field in the electron discharge zone of said tube, end plates adjacent said anode, an external impedance circuit connected between said cathode and said end plates, said circuit having a range of impedance values which extends substantially below the resistance value of the discharge path between the cathode and end plates, and means for continuously varying said external impedance between substantially finite and infinite values thereby to vary the potential difierence between said cathode and said end plates due to the collection of electrons which are attracted to said end plates from the discharge zone.

4. In a signaling system, a magnetron discharge tube having an anode and a cathode, energizing circuits therefor, means for producing a magnetic field in the electron discharge zone of said tube, end plates adjacent said anode, a

variable impedance circuit interconnecting said cathode and said end plates, the impedance values of said circuit being variable over a range which extends substantially from an infinite value to one below the resistance value of the discharge path between the cathode and end plates, and means including a source of modulating potentials for rythmically varying the impedance value of said circuit, thereby to control the electron paths in said discharge zone in such manner that the emissive effects upon said anode are varied by collection of a variable proportion of the total emission on the end plates.

5. A system in accordance with claim 4 and having a gaseous discharge tube and a capacitor in parallel therewith, both being included in said impedance circuit.

6. A system in accordance with claim 4 and having a triode discharge tube included in said impedance circuit, said source of modulating potentials being applied across the input electrodes of said triode discharge tube for varying 'the impedance of the discharge zone therein.

HANS ERICH HOLLMANN. 

